The present invention relates to a coin discrimination apparatus for discriminating authenticity and denominations of coins inserted in public telephones or various kinds of vending machines.
A coin discrimination apparatus of this type is disclosed in, e.g., International Publication No. WO82/02786 (corresponding to Japanese Patent Prepublication No. 58-500263). In this apparatus, discrimination is performed by utilizing oscillation magnetic fields respectively having high and low frequencies which are low enough to allow a coin to be discriminated to pass through magnetic fluxes generated thereby. In this case, a diameter and thickness of a coin are discriminated by the high-frequency magnetic field, while a material of the coin is discriminated by the low-frequency magnetic field. The diameter of coils for discriminating a thickness and a material is smaller than that of a smallest coin to be discriminated. A coil for discriminating a diameter has an elliptic shape having a major axis larger than a diameter of the smallest coin. Discrimination signals can be independently obtained for respective characteristics of a diameter, a thickness, and a material.
In the conventional coin discrimination apparatus described above, independent outputs can be obtained for the respective factors to be discriminated. However, the separate discrimination coils are used for independently discriminating the diameter, thickness, and material of a coin. In this case, a change in output is maximized near the center of each coil at which the magnetic flux is concentrated (i.e., the precision is highest near the center). Assume that coins of two different denominations which are of an identical material and have slightly different diameters are present. In this case, if some material is wound around the smaller-diameter coin to have the same diameter as that of the larger-diameter coin, these coins will be erroneously discriminated as an identical denomination with high probability.